GB2278605A - Flame and smoke retardant polymer compositions - Google Patents

Abstract

Flame and smoke retardant polymer compositions contain a flame and smoke retardant filler and a polymer. The filler comprises magnesium hydroxide and at least one inorganic borate compound with a weight ratio ranging from 16 to 0.2, preferably from 10 to 2.

Description

FLAME AND SMOKE RETARDANT POLYMER COMPOSITIONS This invention relates to flame and smoke retardant polymer compositions. Furthermore, this invention concerns flame and smoke retardant filler to be joined to polymers resulting in said polymer compositions.

Flame and smoke retardant effects of certain filler compounds, supplied for example to polymer compositions build up of polymers, are well-known in the art.

Polymers, generally high molecular weight thermoplastic and thermoset polymers, having utility in the production of articles such as containers for food and drink and parts for the automotive industry or structural members for use in the construction industry and employed as resins respectively, are well known. With regard to polymer compositions employed in a public application, some concern must be shown for the consequences of the polymer compositions catching fire and burning. It is known that some polymers will burn more easily than others.

Polymers such as polyvinylchloride produce, upon combustion, gaseous compounds which have a flame-retarding effect.

When using polymers, which do not produce flame retardant gaseous compounds upon combustion, it is usual to mix said polymers with compounds which have the capability to increase the ignition resistance, to counter the growth of the fire, and to suppress formation of smoke. Since such compounds are added to the above polymers they are generally referred to as flame and smoke retardant fillers.

Generally two main problems are addressed in this field of application. The first one is the effect of flame and smoke retardancy. The flame retarding effect of such fillers generally stems from a chemical reaction of said compounds at an elevated temperature, e.g. decomposition, which requires thermal energy thus restricting the amount of thermal energy available for flame propagation. Furthermore, generation of flame and smoke retardant substances such as steam, giving dilution of the amount of combustible material, can result. The second one concerns the processability and mechanical properties of polymer compositions when filled with such a filler, which often has proven bad as shown by unsatisfactory strength and modulus parameters.

For example from S. Miyata et al., "Fire-Retarding Polypropylene with Magnesium Hydroxide", Jap. Appl. Pol. Sc., Vol. 25, p. 415-425 (1980), it is known to add preferably at least 57 %w of Mg(OH)2 to polypropylene, resulting in a non-flammable composition. When compared with addition of the same amount of A1(OH)3 improved retardancy and mechanical properties were obtained However, in spite of long times to ignition observed for Mg(OH)2, its great rate of heat release is a problem as to the retardancy in development of flames and smoke.

From US 3,865,760 it is known to add for example colemanite, or aluminium trihydrate, or a combination of said compounds to rubber or polymers. However, neither substantial differences in oxygen indices (taken as measure as to their flammability) between the above options, nor improved processability of said materials, which is highly preferred because of its high filling ratio, i.e.

150 phr (parts per hundred resin), have been observed.

So it is the object of the invention to provide flame and smoke retardant polymer compositions composed from flame and smoke retardant fillers and polymers and having improved flame and smoke retardancy characteristics.

It is a further object of the invention to provide flame and smoke retardant fillers for joining with polymers in order to obtain flame and smoke retardant polymer compositions having simultaneously satisfactory flame and smoke retardancy and improved mechanical features.

Now it has been found surprisingly that replacement of a part of magnesium hydroxide by borate compounds results in mixtures giving improved flame and smoke retardancy.

Therefore in accordance with the invention flame and smoke retardant polymer compositions contain a flame and smoke retardant filler and a polymer, said filler comprising magnesium hydroxide and at least one inorganic borate compound with a weight ratio in the range from 16 to 0.2, preferably in the range from 10 to 2. In a further embodiment magnesium hydroxide and a combination of inorganic borate compounds are contained.

In a preferred embodiment of the invention the weight ratio of polymer and filler ranges from 0.4 to 2.5.

Furthermore the invention relates to the flame and smoke retardant filler as shown above, and to products made of the above presented flame and smoke retardant polymer compositions.

In more detail magnesium hydroxide used in this invention suitably has an average particle size in the range of 0.2-20 pm, more preferably in the range of 0.5-8 pm and BET specific surface 2 area in the range of 1-50 m2/g, more preferably in the range of 2 2-20 m2/g. Examples of magnesium hydroxide are naturally occurring brucite, or those prepared by precipitation from various Mg containing solutions, such as sea water, natural brines or industrial effluents with various bases, e.g. slaked lime, dolime, alkali metal hydroxides, aqueous and/or gaseous ammonia or those prepared by hydrothermal recrystallization of Mg(OH)2 precipitate, or those prepared by spray roasting of Mg containing solutions followed by hydration.Magnesium hydroxides of this invention may be used as such or surface treated with various organic coatings known in the art. For example, various fatty acids and their derivatives, silanes, siloxanes, titanates and zirconates can be used. It is generally known that such coatings improve dispersability of the hydroxide into the polymer.

Inorganic borates used in this invention suitably have an average particle size in the range of 0.2-20 Hm, more preferably in the range of 0.5-10 Hm and BET specific surface area in the range 2 2 of 1-20 m2/g, more preferably in the range of 1-15 m /g. For the present invention especially metal borates are applied. Examples of such borates are naturally occurring colemanite (Ca2B6011. 5H20), ulexite (Na2Ca2B10018.l6H20), inderite (Mg2B6Oll.15H2O) or synthetic borates such as zinc borate (2Zn0.3B203. 3H2O), calcium borate (CaB6010. 4H20), magnesium borate, ammonium borate ((NH4)2B407.4H2O).Borates as applied in this invention may be used as such or surface treated with various organic coatings commonly used for the treatment of fillers for polymers. For example, various fatty acids and their derivatives, silanes, siloxanes titanates and zirconates can be used. These coatings also improve dispersability of the borates into the polymer.

The weight ratio of magnesium hydroxide to borate in the mixture ranges from 16:1 to 0.2:1, preferably from 10:1 to 2:1.

Under the term "mixture" in this invention both the physically mixed components (dry or wet) and in situ precipitated or coprecipitated components are comprised. When in situ precipitation or coprecipitation is used, the components in the "mixture" can exist as two separate phases or one phase can be distributed evenly in the other phase or one phase can coat the surface of the other phase.

In the flame and smoke retardant polymer compositions of the present invention a wide range of polymer compounds can be employed. Examples of such polymer compounds include olefin polymers and copolymers such as polyethylene, polypropylene, ethylene/propylene copolymer, ethylene/propylene/diene copolymer; vinyl acetate-type polymers or copolymers such as ethylene/vinyl acetate copolymer; polyamide polymers; polycarbonate polymers polyketone polymers; thermoplastic rubbers such as styrene-butadiene block copolymers and their hydrogenated analogs; and resins, such as epoxies and unsaturated polyesters.

The flame and smoke retardant polymer composition of the present invention suitably contains 100 parts by weight of the above polymer and 250 to 40 parts by weight of the filler mixture, resulting in weight ratios of polymer and filler ranging from 0.4:1 to 2.5:1. This polymer composition can be produced by ordinary kneading methods using a two roll-mill, Banbury (Banbury is a trademark) mixer, single- and/or twin-screw extruder etc.

The present invention will be explained hereinafter more in detail by reference to the following Examples.

In the Examples the following methods for the measurement of particle size distribution (PSD), specific surface area (SSA), and flammability, are used.

PSD measurements were carried out by sedimentation method with Sedigraph 5100 (Sedigraph is a trademark) from Micromeritics. The samples were dispersed in Sedisperse All (hydrocarbon liquid) (Sedisperse is a trademark) and deagglomerated by ultrasonic treatment for 5 minutes at 200 W. A cumulative distribution of mass-percent less than diameter was obtained.

SSA was measured by nitrogen adsorption according to BET method using the automated surface area analyser Gemini 2360 (Gemini is a trademark) from Micromeritics.

Flammability and smoke evolution tests were carried out in Cone Calorimeter (Cone Calorimeter is a trademark) from PL Thermal Sciences Ltd., according to ASTM E1354-90 which further defines instructions and parameters (time to ignition, TTI; total heat release, THR; rate of heat release, RHR; specific extinction area, SEA) for such tests. The specimens for this measurement were prepared from the compositions by compression moulding into plates with the nominal dimensions l00x100x5 mm. The test specimens were 2 tested horizontally at a heat flux of 35 kW/m Use of Cone Calorimeter for the measurement of flammability and smoke evolution is the preferred test method. Among the small scale tests available, the conditions of the Cone Calorimeter test have appeared to approach a real fire situation most closely.

As to flammability characteristics rate of heat release (RHR) is considered the most important parameter to characterise the fire hazard. In particular total heat release (THR) values are considered.

Furthermore, time to ignition (TTI) values and values of specific extinction areas and related peak values (pSEA) as to smoke evolution are measured.

For some examples further details are explained in detail with aid of figures 1A, B and figures 2A, B, wherein: figures 1A and 1B show the rate of heat release as function of time for polypropylene filled, respectively with only magnesium hydroxide and with a filler in accordance with the invention, and figures 2A and 2B show the smoke evolution as function of time for polypropylene filled, respectively with only magnesium hydroxide and with a filler in accordance with the invention.

EXAMPLE 1 150 parts of commercially available coated magnesium hydroxide (Kisuma 5B, a fatty acid compound; Kisuma is a trademark) (MH1), 2 having an average particle size of 6 pm and SSA of 5.4 m /g was compounded with 100 parts of polypropylene (PP) in a Banbury mixer at 180 "C. The torque resulting from the compounding operation and increase of the temperature in the mixing chamber above the set value was continuously monitored. The composition obtained was then compression moulded into specimens used for flammability tests. The results of flammability tests are given in Table 1 as presented hereinafter.

EXAMPLE 2 The procedure of Example 1 was repeated, but magnesium hydroxide was replaced with 150 parts of 3:1 mixture of magnesium hydroxide from Example 1 and colemanite (gaul). Colemanite used in this example had an average particle size of 9 pm and SSA of 2 3.1 m /g.

EXAMPLE 3 The procedure of Example 2 was repeated, but the weight ratio of magnesium hydroxide to colemanite was 1:1.

EXAMPLE 4 The procedure of Example 2 was repeated, but the colemanite was replaced with zinc borate (ZnB). The zinc borate used in this 2 example had an average particle size of 6 pm and SSA of 1.3 m /g.

EXAMPLE 5 The procedure of Example 3 was repeated, but the colemanite was replaced with zinc borate.

EXAMPLE 6 The procedure of Example 2 was repeated, but the loading of 3:1 filler mixture was decreased from 150 parts per 100 parts of polymer to 100 parts per 100 parts of polymer.

EXAMPLE 7 An uncoated grade Mg(OH)2, having a mass-average particle size 2 2' of 1 pm and SSA of 7 m /g, was coated according to the following procedure: 1000 g Mg(OH)2 was suspended in 3500 ml demineralised water.

250 ml solution of sodium oleate (100 g/l) was added into the slurry and mixed at 80 C for 1 hour. The slurry obtained was then diluted to 15 % (m/m) solids and spray dried. In table 2 the obtained Mg(OH)2 is referred to as MH2.

EXAMPLE 8 Ground colemanite having a mass-average particle size of 2 pm 2 and SSA of 8 m /g was suspended in demineralised water to form a dispersion with about 30% (m/m) solids. Solution of sodium oleate (100 g/l) was then added so that 1.9% (m/m on solids) coating was applied to the filler. The suspension was then mixed at 80 "C for 1 hour and spray dried. In table 2 the obtained colemanite is referred to as CaB2.

EXAMPLE 9 Example 1 was repeated, except that magnesium hydroxide from Example 7 was used. The results of flammability are given in Table 2 as presented hereinafter.

EXAMPLES 10-14 Magnesium hydroxide of Example 7 was mixed with colemanite from Example 8 in the ratios given in Table 2. 150 parts of each filler mixture was compounded with 100 parts of polypropylene using the procedure given in the foregoing examples. The test results are also summarized in Table 2.

From Table 1 it is shown clearly that replacement of colemanite or zinc borate on account of magnesium hydroxide results in substantially decreased smoke evolution (pSEA) and total heat released (THR). In particular THR is of great importance since said heat has great effect on start of ignition as explained hereinbefore. Furthermore, as to Example 6 even a reduced amount of filler means an improvement as shown above.

In Table 2 also such improvements can be seen. Although a proportional reduction of TTI is observed, surprisingly THR-values 2 are stabilizing around an average of about 46 MJ/m after 10 minutes which means a correspondingly proportional improvement.

Further to the above it will be clear to those skilled in the art that a right balance can be found which is highly dependant on the specific use and application of the filler and polymer.

For the above examples 9 and 11 in figures 1A, B and 2A, B rate of heat release and smoke evolution are presented as function of time.

2 In figures 1A, B rate of heat release is given in kW/m . As can be seen from these figures, advantageously the rate of heat release is smeared out over a substantially longer time period when the mixture of example 11 is employed.

In figures 2A, B smoke evolution is conventionally given as 2 specific extinction area in m /kg. As can be seen from these figures, advantageously smoke evolution is significantly lower when the mixture of example 11 is used.

From the foregoing description various modifications of the present invention will be apparent to those skilled in the art.

Such modifications are also within the scope of the present invention.

TABLE 1 Results of flammability tests with Cone Calorimeter of PP filled with various fillers at different loadings Ex. Loading, parts TTI, pSEA, THR after X minutes (compared to 100 from ignit., MJ/m2 parts of copolymer) 2 MHl CaBl ZnB s m /kg 2 4 6 10 1 150 - - 121 580 14 27 38 57 2 112.5 37.5 - 91 121 11 20 30 48 3 75 75 - 59 148 11 20 29 48 4 112.5 - 37.5 93 339 12 24 34 54 5 75 - 75 69 314 12 22 32 51 6 75 25 - 86 383 14 26 35 52 TABLE 2 Results of flammability tests with Cone Calorimeter of PP filled with 150 parts filler Ex. Loading, parts TTI, pSEA, THR after X minutes 2 (compared to 100 from ignit., MJ/m parts of polymer) 2 MH2 CaB2 s m /kg 2 4 6 10 9 150 - 153 695 15 29 41 61 10 140 10 112 n.d. 11 21 29 42 11 131 19 101 168 11 20 29 47 12 112 38 85 141 11 21 30 48 13 94 56 80 146 11 20 28 43 14 75 75 75 125 11 22 33 50

Claims (10)

1. CLAIMS 1. Flame and smoke retardant polymer composition containing a flame and smoke retardant filler and a polymer, said filler comprising magnesium hydroxide and at least one inorganic borate compound with a weight ratio ranging from 16 to 0.2, preferably from 10 to 2.
2. 2. Polymer composition as claimed in claim 1, wherein the weight ratio of polymer and filler ranges from 0.4 to 2.5.
3. 3. Polymer composition as claimed in claim 1 or 2, wherein the inorganic borate compound is a metal borate compound.
4. 4. Polymer composition as claimed in claim 3, wherein the metal borate compound is colemanite.
5. 5. Polymer composition as claimed in claim 3, wherein the metal borate compound is zinc borate.
6. 6. Polymer composition as claimed in claim 1 or 2, wherein the inorganic borate compound is ammonium borate.
7. 7. Polymer composition as claimed in any one of the foregoing claims, wherein the magnesium hydroxide has an average particle size in the range of 0.2-20 Hm and a specific surface area in the 2 range of 1-50 m /g.
8. 8. Polymer composition as claimed in any one of the foregoing claims, wherein the inorganic borate compounds have an average particle size in the range of 0.2-20 zm and a specific surface area 2 in the range of l-20 m /g.
9. 9. Flame and smoke retardant filler for joining with a polymer, the filler comprising magnesium hydroxide and at least one inorganic borate compound with a weight ratio ranging from 16 to 0.2, preferably from 10 to 2.
10. 10. Products made of flame and smoke retardant polymer compositions as claimed in any one of the claims l to 8.